The present disclosure relates to a method of fabricating a wafer for use in a semiconductor device, and more particularly, to a method of identifying and evaluating a region of various defects present in a monocrystalline silicon ingot or a silicon wafer.
In general, a silicon wafer is fabricated using a floating zone (FT) process or a CZochralski (CZ) process. The CZ process is most widely used to fabricate a silicon wafer. In the CZ process, polycrystalline silicon is placed into a quartz crucible. The polycrystalline silicon is heated and molten by graphite exothermic material, and a seed crystal immersed into the molten silicon. A monocrystalline silicon ingot is grown by pulling up the immersed seed crystal while rotating the same. The grown silicon ingot is sliced, etched, and polished into a silicon wafer.
The monocrystalline silicon ingot or the silicon wafer may have crystal defects such as Crystal Originated Particles (COP), Flow Pattern Defects (FPD), Oxygen induced Stacking Fault (OiSF), and Bulk Micro Defect (BMD), which are called grown-in defects. There is a need for reducing the concentration and size of the grown-in defects. The crystal defects affect the quality and production yield of devices. Therefore, it is very important to remove the crystal defects and to evaluate the crystal defects easily and quickly.
Depending on the crystal growth conditions, the silicon wafer or the monocrystalline silicon includes a V-rich region where vacancy-type point defects are prevalent and condensed (cluster) defects of supersaturated vacancies are present, a Pv region where vacancy-type point defects are prevalent but no cluster defect is present, a vacancy/interstitial (V/I) boundary, a Pi region where interstitial point defects are prevalent but no cluster defect is present, and an I-rich region where interstitial point defects are prevalent and cluster defects of supersaturated interstitial silicon are present. Detecting how the above regions change depending on their positions and the crystal length of the monocrystalline silicon ingot is fundamental to evaluating the quality of the crystal.
There have been several methods for identifying the defect region of the monocrystalline silicon. In a first method, the COP distribution of a polished and cleaned wafer is evaluated using a particle counter. In a second method, FPD evaluation is performed using a wet etchant for Secco etching. In a third method, an oxygen precipitate is created by high-temperature/long-time heat treatment and the evaluation is performed using a difference between precipitate behaviors of different defect regions. In a fourth method, low-concentration contamination using transition metal and diffusion heat treatment are performed and then the recombination lifetime is measured.
However, in the first method, the wafer must be cleaned by polishing and cleaning prior to estimation. Therefore, several subsequent processes must be performed after the growth of the monocrystal, which increases the required time and also requires a high-cost particle counter for estimation.
In the second method, a selective etchant must be prepared that can provide a suitable etching rate, can be applied to all crystal surfaces, and does not contain environmental toxic materials.
The third method has several drawbacks in terms of the required time for evaluation, the required cost for high-temperature heat treatment, and high-cost equipment. Also, the third method cannot identify a crystal defect region in the case of a sample with an oxygen concentration of less than 10 ppma (New ASTM standards).
An example of the fourth method is the Korean Patent Publication No. 2005-0067417, which discloses a method for measuring the distribution of point defects in a monocrystalline ingot to evaluate only the state of the ingot. In detail, the ingot is sliced in the axial direction. Thereafter, two samples are contaminated with two or more metal elements (e.g., Cu, Ni, Fe, and Co) at a low contamination concentration. Thereafter, heat treatment is performed to create a recombination center in the silicon. Thereafter, the recombination lifetime is measured to measure the distribution of point defects. In this method, the contamination results of two metal elements must be synthesized in order to interpret the crystal defects. Also, the measurement is impossible when a metal precipitate or a haze is generated on the surface thereof. Therefore, the method is restricted in terms of the metal contamination amount and the heat treatment time and contamination concentration must be as low as 1×1012 to 1×1014 atoms/cm2. Also, an additional etching process and an additional analysis device is required when a precipitate is generated.
Furthermore, the conventional methods using selective etching or metal contamination cannot identify the entire crystal defect regions.